Radiation victims who suffer from gastrointestinal injuries are extremely susceptible to gut-associated sepsis. Bacterial translocation does not occur in hosts who are carriers of M1 macrophages (IL-10-IL-12+ M) at the bacterial translocation sites (lamina propria, LP; mesenteric lymph nodes, MLNs). However, M1M are not generated in these organs of mice with whole body ?-irradiation (WBI-mice) even though the majority of M populations are still present in WBI-mice. These mice are carriers of M2bM (CCL1+IL-10+IL-12- M), which inhibit the M conversion from resident M to M1M. CCL1 produced by M2bM has been identified as an essential chemokine for the maintenance of their M2bM properties. In the previous project (NIH 1RC2AI087591-01), we have developed a new gene therapy against gut-associated sepsis in WBI-mice using CCL1 antisense oligodeoxynucleotide (ODN). This ODN regresses M2bM to resident M through the depletion of CCL1 production. Gut-associated sepsis induced by Enterococcus faecalis oral infection is markedly mitigated in WBI-mice multiply treated with CCL1 antisense ODN starting two to three weeks after 4-12 Gy of ?-irradiation. From these results, we have concluded that bacterial translocation and subsequent sepsis in WBI-mice are controllable by CCL1 antisense gene therapy. To establish the benefits of this gene therapy toward clinical application, we need more information in both murine (WBI-mice) and human (a human / mouse chimera model, WBI-chimeras) systems. In Year 1, antibacterial capacities of the gene therapy on controlling endogenous bacterial translocation and subsequent sepsis stemming from intestinal microflora will be determined in 8-13 Gy WBI-mice. In Year 2, the antibacterial spectrum of the gene therapy will be determined in decontaminated WBI-mice (dWBI-mice) orally infected with various species of enteric bacteria. In dWBI-mice, gut-associated sepsis stemming from endogenous intestinal microflora does not develop. In Year 3, gut-associated sepsis caused by E. faecalis oral infection in 4-8 Gy dWBI-mice will be controlled by therapeutic treatment with CCL1 antisense ODN. In Year 4, translational studies will be performed from WBI-mice to humanized WBI-chimeras. In these chimeras, gut-associated sepsis will be controlled by human CCL1 antisense ODN. For the clinical application of the gene therapy, translational studies from mice to humans are essential. For IND application, the publication and presentation of experimental data, as well as the preparation of protocol for clinical testing will be completed in the final year. GLP safety and toxicology testing, will be completed at CPDF.